U.S. patent application number 11/951196 was filed with the patent office on 2008-06-12 for liquid discharging apparatus.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Yoshiko AZAMI, Hirokazu NUNOKAWA.
Application Number | 20080136856 11/951196 |
Document ID | / |
Family ID | 39497458 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080136856 |
Kind Code |
A1 |
AZAMI; Yoshiko ; et
al. |
June 12, 2008 |
LIQUID DISCHARGING APPARATUS
Abstract
A liquid discharging apparatus includes upstream side nozzle
group, a downstream side nozzle group, and a transport mechanism.
The downstream side nozzle group is located on a downstream side in
a transport direction as compared with the upstream side nozzle
group. The transport mechanism transports a medium in the transport
direction to the upstream side nozzle group and to the downstream
side nozzle group. The upstream side nozzle group and the
downstream side nozzle group each are formed of a plurality of
nozzle columns that are arranged in the transport direction. Each
of the nozzle columns is formed so that a plurality of nozzles that
discharge liquid are arranged in a direction that intersects with
the transport direction. A transport speed varies in accordance
with the number of nozzle columns used.
Inventors: |
AZAMI; Yoshiko;
(Matsumoto-shi, JP) ; NUNOKAWA; Hirokazu;
(Matsumoto-shi, JP) |
Correspondence
Address: |
WORKMAN NYDEGGER
60 EAST SOUTH TEMPLE, 1000 EAGLE GATE TOWER
SALT LAKE CITY
UT
84111
US
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
39497458 |
Appl. No.: |
11/951196 |
Filed: |
December 5, 2007 |
Current U.S.
Class: |
347/16 |
Current CPC
Class: |
B41J 2/2128 20130101;
B41J 2/155 20130101; B41J 11/42 20130101 |
Class at
Publication: |
347/16 |
International
Class: |
B41J 29/38 20060101
B41J029/38 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2006 |
JP |
2006-329711 |
Claims
1. A liquid discharging apparatus comprising: an upstream side
nozzle group; a downstream side nozzle group that is located on a
downstream side in a transport direction as compared with the
upstream side nozzle group; and a transport mechanism that
transports a medium in the transport direction to the upstream side
nozzle group and to the downstream side nozzle group, wherein the
upstream side nozzle group and the downstream side nozzle group
each are formed of a plurality of nozzle columns that are arranged
in the transport direction, wherein each of the nozzle columns is
formed so that a plurality of nozzles that discharge liquid are
arranged in a direction that intersects with the transport
direction, and wherein a transport speed varies in accordance with
the number of nozzle columns used.
2. The liquid discharging apparatus according to claim 1, wherein
the transport speed when the number of nozzle columns used is more
than a predetermined number is lower than the transport speed when
the number of nozzle columns used is equal to or smaller than the
predetermined number.
3. The liquid discharging apparatus according to claim 2, wherein
the predetermined number is the number of nozzle columns that the
upstream side nozzle group or the downstream side nozzle group
has.
4. The liquid discharging apparatus according to claim 2, wherein,
when the number of nozzle columns used is more than the
predetermined number, liquid is alternately discharged from the
nozzles of the upstream side nozzle group and from the nozzles of
the downstream side nozzle group.
5. The liquid discharging apparatus according to claim 1, wherein
the nozzle columns used are nozzle columns that face the medium at
the same time.
6. The liquid discharging apparatus according to claim 5, wherein
the transport speed is determined in accordance with the length of
the medium in the transport direction.
7. The liquid discharging apparatus according to claim 1, wherein
the nozzle columns used are nozzle columns that face, at the same
time, an area on the medium, to which liquid is discharged.
8. The liquid discharging apparatus according to claim 7, wherein
the transport speed is determined on the basis of the length of the
area in the transport direction.
9. The liquid discharging apparatus according to claim 1, wherein
the transport speed when liquid is discharged using both the
upstream side nozzle group and the downstream side nozzle group is
lower than the transport speed when liquid is discharged using one
of the upstream side nozzle group and the downstream side nozzle
group.
10. The liquid discharging apparatus according to claim 9, wherein,
when the nozzle columns of the downstream nozzle group are offset
from the nozzle columns of the upstream side nozzle group in the
direction that intersects with the transport direction, the
transport speed when liquid is discharged in a high resolution
using both the upstream side nozzle group and the downstream side
nozzle group is lower than the transport speed when liquid is
discharge in a low resolution using one of the upstream side nozzle
group and the downstream side nozzle group.
11. The liquid discharging apparatus according to claim 1, wherein,
when the upstream side nozzle group and the downstream side nozzle
group each have nozzle columns that discharge first liquid and
nozzle columns that discharge second liquid, the transport speed
when the first liquid and the second liquid are discharged onto the
medium is lower than the transport speed when the first liquid is
discharged onto the medium but the second liquid is not discharged
onto the medium.
12. The liquid discharging apparatus according to claim 1, wherein
the transport speed changes when the medium is being
transported.
13. The liquid discharging apparatus according to claim 1, wherein
the transport speed is determined on the basis of the maximum
number of nozzle columns used.
14. The liquid discharging apparatus according to claim 1, further
comprising: a mechanism that moves the upstream side nozzle group
and the downstream side nozzle group relatively in the transport
direction.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The invention relates to a liquid discharging apparatus.
[0003] 2. Related Art
[0004] An ink jet printer is known as one of liquid discharging
apparatuses. The ink jet printer performs printing on various types
of medium, such as paper, cloth, or film, by discharging ink from
nozzles. Almost all ink jet printers perform printing while moving
a head (nozzles) in a direction that intersects with the transport
direction of a medium (a carriage type printer).
[0005] In recent years, a line head printer, of which a nozzle
column has a length of paper width, the nozzle column being
arranged along a direction that intersects with the transport
direction of a medium, has been developed. The line head printer
performs printing by transporting a medium without moving a head,
so that it is able to perform printing at high speed, which is, for
example, described in Japanese Unexamined Patent Application
Publication No. 2002-240300. However, in the line head printer,
because ink is discharged from multiple numbers of nozzles at the
same time, electric power consumed by the printer increases.
[0006] Then, there has occurred a trouble in which a power failure
process is performed because of a decrease in voltage of a power
supply portion and, as a result, printing is stopped. Then, a
method has been proposed, in which a setting voltage for activating
a power failure process is decreased when ink is discharged from
multiple numbers of nozzles at the same time, which is, for
example, described in Japanese Unexamined Patent Application
Publication No. 5-155117.
[0007] Thus, in the line head printer, there is a possibility that
ink is discharged from multiple numbers of nozzles at the same
time. In this case, because electric power consumption increases,
there has been a problem in which printing is not performed
normally, or the like.
SUMMARY
[0008] An advantage of some aspects of the invention is that it
reduces a maximum electric power consumed by a line head
printer.
[0009] An aspect of the invention provides a liquid discharging
apparatus. The liquid discharging apparatus includes upstream side
nozzle group, a downstream side nozzle group, and a transport
mechanism. The downstream side nozzle group is located on a
downstream side in a transport direction as compared with the
upstream side nozzle group. The transport mechanism transports a
medium in the transport direction to the upstream side nozzle group
and to the downstream side nozzle group. The upstream side nozzle
group and the downstream side nozzle group each are formed of a
plurality of nozzle columns that are arranged in the transport
direction. Each of the nozzle columns is formed so that a plurality
of nozzles that discharge liquid are arranged in a direction that
intersects with the transport direction. A transport speed varies
in accordance with the number of nozzle columns used.
[0010] Other aspects of the invention will be apparent from the
specification and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0012] FIG. 1 is a block diagram of a general configuration of a
printer according to an embodiment of the invention.
[0013] FIG. 2A is a longitudinal cross-sectional view of the
printer. FIG. 2B is a view that shows a state where the printer
transports a sheet of paper.
[0014] FIG. 3 is a view that shows an array of nozzles formed on
the lower face of an upstream side head unit and an array of
nozzles formed on the lower face of a downstream side head
unit.
[0015] FIG. 4 is a view that shows a driving signal generating
circuit.
[0016] FIG. 5 is a view that shows a relationship between a driving
signal and the size of a dot formed by a nozzle.
[0017] FIG. 6 is a view that shows a head driving circuit provided
in a head unit.
[0018] FIG. 7 is a view that illustrates changes in voltage of a
first driving pulse output from the driving signal generating
circuit and changes in electric current flowing through
transistors.
[0019] FIG. 8 is a plan view of a head unit interval of a first
application example.
[0020] FIG. 9A is a view that shows a state where printing is
performed on the rear end side of an A4 size sheet of paper by the
upstream side head unit. FIG. 9B is a view that shows a state where
printing is performed on the front end side and rear end side of an
A4 size sheet of paper by the upstream side head unit and the
downstream side head unit. FIG. 9C is a view that shows a state
where printing is performed on the front end side of an A4 size
sheet of paper by the downstream side head unit.
[0021] FIG. 10 is a view that shows a first comparative example of
which an interval is reduced as compared with the head unit
interval of the first application example.
[0022] FIG. 11A to FIG. 11C are views that show a head unit
interval of a second application example.
[0023] FIG. 12 is a view of a second comparative example of which
an interval is increased as compared with the head unit interval of
the second application example.
[0024] FIG. 13 is a view that shows a state where printing is
performed on an A3 size sheet of paper using the head unit interval
of the first application example.
[0025] FIG. 14 is a view that shows a first driving signal and a
second driving signal.
[0026] FIG. 15 is a flowchart when a printer driver determines a
print method according to a first embodiment.
[0027] FIG. 16 is one example of a flowchart in which the printer
driver determines a print method on the basis of the type of a
printing sheet of paper.
[0028] FIG. 17A is a view that shows a printing area in which an
image is printed on an A3 size sheet of paper.
[0029] FIG. 17B is a view that shows a state where the image is
printed within the printing area on the A3 size sheet of paper.
[0030] FIG. 17C is a view that shows a state where the image is
printed within the printing area on the A3 size sheet of paper.
[0031] FIG. 17D is a view that shows a state where the image is
printed within the printing area on the A3 size sheet of paper.
[0032] FIG. 17E is a view that shows a state where the image is
printed within the printing area on the A3 size sheet of paper.
[0033] FIG. 17F is one example of a relatively small image.
[0034] FIG. 18 is a flowchart that is executed when the printer
driver determines a print method in a first determination example
of a second embodiment.
[0035] FIG. 19 is a flowchart that is executed when the printer
driver determines a print method in a second determination
example.
[0036] FIG. 20 is a flowchart that is executed when the printer
driver determines a print method in a third determination
example.
[0037] FIG. 21A to FIG. 21C are views that show a state where an A3
size sheet of paper is transported.
[0038] FIG. 22A is a view that shows a relationship between the
number of nozzle columns that face an A3 size sheet of paper and
transport time. FIG. 22B is a view that shows changes in transport
speed while printing is being performed on an A3 size sheet of
paper.
[0039] FIG. 23 is one example of a flowchart that is executed in
the case where a plurality of reference items are combined.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
Overview of Disclosure
[0040] At least the following aspects will become apparent from the
description in the specification and the accompanying drawings.
[0041] That is, it is possible to realize a liquid discharging
apparatus that includes an upstream side nozzle group, a downstream
side nozzle group located on a downstream side as compared with the
upstream side nozzle group, and a transport mechanism that
transports a medium to the upstream side nozzle group and to the
downstream side nozzle group in the transport direction, wherein
the upstream side nozzle group and the downstream side nozzle group
each are formed of a plurality of nozzle columns that are arranged
in the transport direction, each of the nozzle columns is formed so
that a plurality of nozzles that discharge liquid are arranged in a
direction that intersects with the transport direction, and a
transport speed varies in accordance with the number of nozzle
columns used. According to the above liquid discharging apparatus,
a liquid discharging mode may be varied in accordance with the
number of nozzle columns used, so that it is possible to reduce the
maximum power consumption. For example, when the number of nozzle
columns used is large, a transport speed is reduced to delay the
timing to discharge liquid. As a result, the number of nozzle
columns from which liquid is discharged at the same time is
reduced, so that the maximum power consumption is reduced. On the
contrary, when the number of nozzle columns used is small, a
transport speed is increased, it does not matter even when liquid
is discharged from all the nozzle columns used at the same time, so
that liquid discharge time may be shortened.
[0042] In the above liquid discharging apparatus, the transport
speed when the number of nozzle columns used is more than a
predetermined number is lower than the transport speed when the
number of nozzle columns used is equal to or smaller than the
predetermined number. According to the above liquid discharging
apparatus, a transport speed is reduced when the number of nozzle
columns used is large and, thereby, the timing to discharge liquid
is delayed, so that it is possible to reduce the maximum power
consumption.
[0043] In the above liquid discharging apparatus, the predetermined
number is the number of nozzle columns that the upstream side
nozzle group or the downstream side nozzle group has. According to
the above liquid discharging apparatus, it is possible to prevent
the maximum power consumption from being larger than power
consumption when liquid is discharged at the same time from all the
nozzle columns that the upstream side nozzle group or the
downstream side nozzle group has.
[0044] In the above liquid discharging apparatus, when the number
of nozzle columns used is more than the predetermined number,
liquid is alternately discharged from the nozzles of the upstream
side nozzle group and from the nozzles of the downstream side
nozzle group. According to the above liquid discharging apparatus,
when the number of nozzle columns used is large, it is possible to
reduce the maximum power consumption.
[0045] In the above liquid discharging apparatus, the nozzle
columns used are nozzle columns that face the medium at the same
time. According to the above liquid discharging apparatus,
irrespective of the size of a medium, it is possible to suppress
the maximum power consumption to a certain value. As the size of a
medium increases, the number of nozzle columns that face the medium
at the same time increases. Then, if liquid is discharged from all
the nozzle columns that face the medium at the same time, the
maximum power consumption becomes large. Therefore, when the number
of nozzle columns that face the medium at the same time is large, a
transport speed is reduced to delay the timing to discharge
liquid.
[0046] In the above liquid discharging apparatus, the transport
speed is determined in accordance with the length of the medium in
the transport direction. According to the above liquid discharging
apparatus, irrespective of the size of a medium, it is possible to
suppress the maximum power consumption to a certain value. When the
length of a medium in the transport direction is large, because the
medium faces the nozzle columns of both the upstream side nozzle
group and the downstream side nozzle group at the same time, a
transport speed is reduced to delay the timing to discharge
liquid.
[0047] In the above liquid discharging apparatus, the nozzle
columns used are nozzle columns that face, at the same time, an
area on the medium, to which liquid is discharged. According to the
above liquid discharging apparatus, even when the size of a medium
is large, however, when an area to which liquid is discharged is
small, liquid is discharged at the same time from nozzle columns
used. Thus, it is possible to shorten liquid discharging time as
much as possible.
[0048] In the above liquid discharging apparatus, the transport
speed is determined on the basis of the length of the area in the
transport direction. According to the above liquid discharging
apparatus, even when the size of a medium is large, it is possible
to shorten liquid discharging time as much as possible.
[0049] In the above liquid discharging apparatus, the transport
speed when liquid is discharged using both the upstream side nozzle
group and the downstream side nozzle group is lower than the
transport speed when liquid is discharged using one of the upstream
side nozzle group and the downstream side nozzle group. According
to the above liquid discharging apparatus, on the basis of the
nozzle columns used, it is possible to suppress the maximum power
consumption to a certain value, and it is possible to shorten
liquid discharging time as much as possible. For example, when one
of the upstream side nozzle group and the downstream side nozzle
group is used, the number of nozzle columns used is small. Thus, by
increasing the transport speed, it is possible to discharge liquid
at the same time from all the nozzle columns used.
[0050] In the above liquid discharging apparatus, when the nozzle
columns of the downstream nozzle group are offset from nozzle
columns of the upstream side nozzle group in the direction that
intersects with the transport direction, the transport speed when
liquid is discharged in a high resolution using both the upstream
side nozzle group and the downstream side nozzle group is lower
than the transport speed when liquid is discharged in a low
resolution using one of the upstream side nozzle group and the
downstream side nozzle group. According to the above liquid
discharging apparatus, on the basis of nozzle columns used, it is
possible to suppress the maximum power consumption to a certain
value, and it is possible to shorten liquid discharging time when
liquid is discharged in a low resolution.
[0051] In the above liquid discharging apparatus, when the upstream
side nozzle group and the downstream side nozzle group each have
nozzle columns that discharge first liquid and nozzle columns that
discharge second liquid, the transport speed when the first liquid
and the second liquid are discharged onto the medium is lower than
the transport speed when the first liquid is discharged onto the
medium but the second liquid is not discharged onto the medium.
According to the above liquid discharging apparatus, even when the
number of types of liquid discharged is small (for example,
monochrome printing), and even when the number of types of liquid
discharged is large (for example, color printing), it is possible
to suppress the maximum power consumption to a certain value. In
addition, when in monochrome printing, it is possible to shorten
liquid discharging time.
[0052] In the above liquid discharging apparatus, the transport
speed changes when the medium is being transported. According to
the above liquid discharging apparatus, the transport speed changes
on the basis of the number of used nozzle columns, which varies
while a medium is being transported. Therefore, it is possible to
shorten liquid discharging time as compared with transport is
performed at a constant transport speed.
[0053] In the above liquid discharging apparatus, the transport
speed is determined on the basis of the maximum number of nozzle
columns used. According to the above liquid discharging apparatus,
because the transport speed does not change while a medium is being
transported, control becomes easy.
[0054] In the above liquid discharging apparatus, a mechanism that
moves the upstream side nozzle group and the downstream side nozzle
group relatively in the transport direction is provided. According
to the above liquid discharging apparatus, the maximum power
consumption is suppressed to a certain value on the basis of paper
size to be printed, types of printable paper size increase.
Configuration of Line Head Printer and Printing Method
[0055] In an embodiment, a line head printer (hereinafter, printer
1) from among ink jet printers will be described, for example. FIG.
1 is a block diagram of a general configuration of the printer 1
according to the embodiment. FIG. 2A is a longitudinal
cross-sectional view of the printer 1. FIG. 2B is a view that shows
a state where the printer 1 transports a sheet of paper S
(medium).
[0056] The printer 1 receives print data from a computer 30, which
is an external device, and controls various units (a transport unit
10, a head unit 20) by a controller 50 and then forms an image on
the sheet of paper S. In addition, a group of detectors 40 monitors
status inside the printer 1 and, on the basis of the detected
result, the controller 50 controls various units.
[0057] The controller 50 is a control unit for controlling the
printer 1. An interface portion 51 is used to transmit and receive
data between the computer 30, which is an external device, and the
printer 1. A CPU 52 is a processing unit for executing control over
the entire printer 1. A memory 53 is used to secure an area that
stores a program of the CPU 52, a work area, and the like. The CPU
52 controls various units using a unit control circuit 54 in
accordance with a program stored in the memory 53.
[0058] A transport unit 10 feeds a sheet of paper S to a printable
position and transports the sheet of paper S by a predetermined
amount of transport in the transport direction during printing. A
paper feed roller 13 is a roller that is used for automatically
feeding a sheet of paper S, which is inserted into a paper
insertion portion, onto a transport belt 12 within the printer 1.
Then, an annular transport belt 12 is rotated by both transport
rollers 11A, 11B, and the sheet of paper S placed on the transport
belt 12 is transported. Note that the sheet of paper S is
electrostatically adsorbed or vacuum adsorbed to the transport belt
12 (not shown).
[0059] A head unit 20 is used for discharging ink onto a sheet of
paper S. The head unit 20 includes a plurality of heads 21 and a
head driving circuit 22. Each of the heads 21 has a plurality of
nozzles, which are ink discharging portions. Each of the nozzles is
provided with an ink chamber (not shown) that contains ink and a
driving element (piezoelectric element PZT) that is used for
discharging ink by varying the volume of the ink chamber. Moreover,
the printer 1 of the embodiment includes two head units 20 (an
upstream side head unit 20A and a downstream side head unit 20B).
The upstream side head unit 20A is fixed at a position near the
upstream side transport roller 11A. The downstream side head unit
20B is fixed at a position near the downstream side transport
roller 11B. Then, the upstream side head unit 20A and the
downstream side head unit 20B are arranged at a predetermined
interval X in the transport direction.
[0060] The group of detectors 40 includes a rotary encoder, a paper
detecting sensor 41, an optical sensor, and the like.
Printing Procedure
[0061] The controller 50, when receiving a print instruction and
print data from the computer 30, analyzes the content of various
commands included in the print data and performs the following
processes using various units.
[0062] First, the controller 50 rotates the paper feed roller 13 to
feed a sheet of paper S to be printed, onto the transport belt 12.
Then, the controller 50 rotates the transport rollers 11A, 11B to
position the fed sheet of paper S to a print start position. At
this time, the sheet of paper S faces at least part of nozzles of
the upstream side head unit 20A.
[0063] Next, the sheet of paper S is transported at a constant
speed on the transport belt 12 and is passed below the upstream
side head unit 20A and the downstream side head unit 20B. While the
sheet of paper S is being passed below the head units 20, ink is
intermittently discharged from the nozzles. As a result, a dot
column (raster line) formed of a plurality of dots is formed on the
sheet of paper S along the transport direction.
[0064] Finally, the controller 50 delivers the sheet of paper S,
which has finished printing an image, from the transport roller
11B.
Lower Face of Head Unit 20
[0065] FIG. 3 is a view that shows an array of nozzles formed on
the lower face of the upstream side head unit 20A and an array of
nozzles formed on the lower face of the downstream side head unit
20B. Each of the head units 20 includes multiple (n) heads 21.
Then, the multiple heads 21 are arranged in a staggered manner in a
paper width direction that intersects with the transport direction.
The heads that belong to the upstream side head unit 20A are
denoted by 21A. The heads that belong to the downstream side head
unit 20B are denoted by 21B. Then, The head are assigned with
consecutive numbers in order from the left side, suffixing the
number with parenthesis, that is, a first head 21(1), a second head
21(2), and the like. For example, the leftmost head of the upstream
side head unit 20A is defined as an upstream side first head
21A(1).
[0066] On the lower face of each head 21, a yellow ink nozzle
column Y, a magenta ink nozzle column M, a cyan ink nozzle column
C, and a black ink nozzle column K are formed. Each of the nozzle
columns is provided with 360 nozzles, and smaller numbers are
suffixed to nozzles the more the nozzles are located at the left
side in each nozzle column (#i=1 to 360). Then, the nozzles of each
nozzle column are aligned at constant intervals D (nozzle pitch D)
in the paper width direction.
[0067] In each of the head units 20, the heads 21 are arranged so
that the interval between the nozzle #360 of a left side head 21
and the nozzle #1 of a right side head 21, which are arranged
adjacently in the paper width direction, becomes the nozzle pitch
D. For example, the interval between the nozzle #360 of the
downstream side second head 21B(2) and the nozzle #1 of the
downstream side third head 21B(3) is the nozzle pitch D. Note that
the length of each nozzle column is 1 inch, and the nozzle pitch D
is 360 dpi.
[0068] Accordingly, nozzles are arranged at constant intervals D in
the paper width direction from the leftmost nozzle #1 of the
leftmost first head 21A(1) of the upstream side head unit 20A to
the right most nozzle #360 of the right most n-th head 21A(n)
thereof. Similarly, nozzles are arranged at constant intervals D in
the paper width direction from the leftmost nozzle #1 of the
leftmost first head 21B(1) of the downstream side head unit 20B to
the right most nozzle #360 of the right most n-th head 21B(n)
thereof.
[0069] In addition, the nozzles of the upstream side head unit 20A
are offset to the right side relative to the nozzles of the
downstream side head unit 20B by a half of the nozzle pitch D
(1/2D). For example, the nozzle #2 of the upstream side second head
21A(2) is arranged offset to the right side relative to the nozzle
#2 of the downstream side second head 21B(2) in the paper width
direction by 1/2D.
[0070] In the printer 1 (line head printer), a sheet of paper S is
transported and printed so that the nozzle faces of the fixed head
units 20 face the sheet of paper S. When the sheet of paper S is
printed with a resolution of 720 dpi.times.720 dpi, an image of 360
dpi is printed in the paper width direction in such a manner that
the sheet of paper S is passed below the upstream side head unit
20A. Then, as the sheet of paper S is passed below the downstream
side head unit 20B, an image of 360 dpi is printed at a position
that is offset from a position of the preceding printed image by a
half nozzle pitch to the right side in the paper width direction.
That is, the image of 720 dpi is printed in the paper width
direction by the upstream side head unit 20A and the downstream
side head unit 20B. At this time, the transport speed of the sheet
of paper S is determined so that an image in the transport
direction becomes 720 dpi.
[0071] Note that the head units 20 are fixed and not moved in the
paper width direction, the maximum length of a sheet of paper S in
the paper width direction, which is printable by the printer 1,
will be a length Y. The length Y is a length from the nozzle #1 of
the leftmost first head 21B(1) of the downstream side head unit 20B
to the nozzle #360 of the rightmost n-th head 21A(n) of the
upstream side head unit 20A.
[0072] In the present embodiment, the length Y is made greater than
the long side 297 mm of A4 size sheet of paper (=210.times.297 mm).
For example, when the length of a nozzle column is 1 inch (=25.4
mm), it means that at least twelve (297/25.4=11.7) or more head 21
are arranged in the paper width direction in each of the head units
20 in a staggered manner. Then, when A4 size sheet of paper is
printed, it is only necessary to feed a sheet of paper so that the
long side of the sheet is parallel to the paper width
direction.
[0073] In addition, A3 size sheet of paper (=297.times.420), which
has twice the size of A4 size sheet of paper, may be printed by
feeding the short side of a sheet of paper so as to be parallel to
the paper width direction. That is, the maximum size of a sheet of
paper S that is printable by the printer 1 of the present
embodiment is A3 size.
Driving Signal Generating Circuit 60
[0074] FIG. 4 is a view that shows a driving signal generating
circuit 60. The driving signal generating circuit 60 is included in
the unit control circuit 54, and includes a waveform generating
circuit 61 and an amplifier circuit 62. Then, in the driving signal
generating circuit 60, a driving signal DRV is generated on the
basis of waveform information stored in the memory 53.
[0075] The amplifier circuit 62 includes an upward transistor (NPN
transistor) Q1 that operates when a voltage of the driving signal
DRV rises and a downward transistor (PNP transistor) Q2 that
operates when a voltage of the driving signal DRV falls. The
collector of the upward transistor Q1 is connected to a power
source, and the emitter of the upward transistor Q1 is connected t
an output signal line of the driving signal DRV. The collector of
the downward transistor Q2 is connected to a ground (earth), and
the emitter of the downward transistor Q2 is connected to the
output signal line of the driving signal DRV.
[0076] By the waveform generating circuit 61, waveform information,
which is a digital signal, is converted into a waveform signal,
which is an analog signal, and output to the amplifier circuit 62.
This waveform signal controls the amplifier circuit 62. As the
upward transistor Q1 enters an ON state by the waveform signal, the
driving signal DRV rises. On the other hand, as the downward
transistor Q2 enters an ON state by the waveform signal, the
driving signal DRV falls. In this manner, the driving signal DRV is
output from the connecting point on the emitter sides of the two
transistors Q1 and Q2.
[0077] Note that the driving signal DRV is feedbacked (FB) to the
waveform generating circuit 61. That is, the waveform generating
circuit 61 generates a waveform signal in consideration of a
difference between a voltage value of a target driving signal DRV
and a voltage value of an actual driving signal DRV.
Driving Signal DRV and Forming of Dots
[0078] FIG. 5 is a view that shows a relationship between a driving
signal DRV and the size of a dot formed by a nozzle. The driving
signal DRV has a first driving pulse W1 and a second driving pulse
W2. The shape of the driving pulses is determined in accordance
with the amount of ink discharged from a nozzle.
[0079] FIG. 6 is a view that shows a head driving circuit 22 in
each of the head units 20. Note that the parenthetic numeral in the
drawing denotes a number of the nozzle to which a member or a
signal corresponds. When a print signal is transmitted to the head
driving circuit 22, the switch control signal generating circuit 24
generates a switch control signal SW(i) in accordance with image
data of one pixel (a rectangular area that is virtually defined on
a sheet of paper S) that is allocated to each nozzle #i. This
switch control signal SW(i) executes on/off control of each switch
23(i) corresponding to each piezoelectric element PZT(i). Then, the
on/off operation of the switch 23 applies or interrupts the driving
signal DRV to the corresponding piezoelectric element PZT.
[0080] For example, when the level of the switch control signal
SW(i) is "1", the switch 23(i) turns on and passes a driving pulse
of the driving signal DRV as it is. Thus, the driving pulse is
applied to the piezoelectric element PZT(i). Then, when the driving
pulse is applied to the piezoelectric element PZT(i), the
piezoelectric element PZT(i) deforms in accordance with the driving
pulse and, thereby, an elastic film (side wall) that partly defines
the ink chamber deforms, so that a prescribed amount of ink in the
ink chamber is discharged from the nozzle #i. On the other hand,
when the level of the switch control signal SW(i) is "0", the
switch 23(i) turns off and blocks the driving pulse of the driving
signal DRV.
[0081] As shown in FIG. 5, when the switch control signal SW(i) is
"11", the first driving pulse W1 and the second driving pulse W2
are applied to the piezoelectric element PZT(i). Then, a prescribed
amount of ink is discharged from the nozzle #i, and a large dot is
formed. Similarly, when the switch control signal SW(i) is "10", a
medium dot is formed. When the switch control signal SW(i) is "01",
a small dot is formed. Furthermore, when the switch control signal
SW(i) is "00", no driving pulse is applied to the piezoelectric
element PZT(i), so that the piezoelectric element PZT(i) does not
deform and, as a result, no dot is formed.
Driving Signal DRV and Power Consumption
[0082] FIG. 7 is a view that illustrates changes in voltage of the
first driving pulse W1 output from the driving signal generating
circuit 60 and changes in current flowing through transistors Q1
and Q2. Hereinafter, a relationship between a driving pulse and
power consumption will be described by taking the first driving
pulse W1 for example.
[0083] The driving signal generating circuit 60 maintains an
intermediate voltage Vc until the time T0. Then, between the time
T0 and the time T1, the driving signal generating circuit 60
reduces a voltage from the intermediate voltage Vc to the minimum
voltage V1. At this time, the downward transistor Q2 enters an ON
state, and an electric current i2(A) flows through the downward
transistor Q2. Then, the piezoelectric element PZT expands the
volume of the ink chamber.
[0084] After that, the driving signal generating circuit 60, after
maintaining the minimum voltage V1 until the time T2, increases the
voltage to the maximum voltage Vh between the time T2 to the time
T3. At this time, the upward transistor Q1 enters an ON state, and
an electric current i1(A) flows through the upward transistor Q1.
Then, the piezoelectric element PZT discharges ink droplets from
the nozzle by contracting the volume of the ink chamber.
[0085] Finally, the driving signal generating circuit 60 maintains
the maximum voltage Vh until the time T4 and reduces the voltage to
the intermediate voltage Vc between the time T4 and the time T5. At
this time, the downward transistor Q2 enters an ON state, and an
electric current i2(A) flows through the downward transistor Q2.
Then, the piezoelectric element PZT expands the volume of the ink
chamber to return the volume of the ink chamber to an original
volume.
[0086] In this manner, when the first driving pulse W1 is applied
to the piezoelectric element PZT, electric current flows through
the upward transistor Q1 and the downward transistor Q2. Thus,
power is consumed.
[0087] An electric current i1(A) flows through the upward
transistor Q1 between the time T2 and the time T3. Therefore, power
consumed at time Tx between the time T2 and the time T3 may be
calculated by multiplying the electric current i1(A) by a
difference in potential between the potential of the driving signal
DRV at the time Tx and a power source potential Vmax. Then, the sum
of power consumption from the time T2 to the time T3 is an electric
energy q1 (Wh) consumed by the upward transistor Q1 when the first
driving pulse W1 is applied to the piezoelectric element PZT.
[0088] An electric current i2(A) flows through the downward
transistor Q2 between the time T0 and the time T1 and between the
time T4 and the time T5. Therefore, power consumption at time Ty
between the time T0 and the time T1 or between the time T4 and the
time T5 is calculated by multiplying the electric current i2(A) by
a difference in potential between the driving signal DRV at the
time Ty and a ground (GND) potential. Then, the sum of power
consumption from the time T0 to the time T1 and from the time T4 to
the time T5 is an electric energy q2 (Wh) consumed by the downward
transistor Q2 when the first driving pulse W1 is applied to the
piezoelectric element PZT.
[0089] That is, an electric energy consumed when the first driving
pulse W1 is applied to a single piezoelectric element PZT is q1+q2
(Wh), which is obtained by adding the electric energy q1 (Wh)
consumed by the upward transistor Q1 and the electric energy q2
(Wh) consumed by the downward transistor Q2. Note that a period of
time during which the driving pulse W is applied to the
piezoelectric element PZT (in FIG. 7, from T0 to T5) is minute.
Therefore, it is conceivable that power consumption increases at a
moment when the driving pulse W is applied to the piezoelectric
element PZT.
[0090] Then, an electric energy consumed when the first driving
pulse W1 is applied to N numbers of the piezoelectric elements PZT
at the same time is (q1+q2).times.N (Wh). That is, at a moment when
the first driving pulse W1 is applied to the large numbers of the
piezoelectric elements PZT at the same time, power consumption
rapidly increases. Thus, as the number of nozzles that discharge
ink at the same time increases, power consumption increases.
[0091] Note that a medium dot and a small dot are formed so that
respective driving pulses are applied to the piezoelectric element
PZT; however, a large dot is formed so that two driving pulses (W1
and W2) are applied to the piezoelectric element PZT. Therefore,
power consumed when a large dot is formed is larger than power
consumed when a medium dot or a small dot is formed. That is, as
the number of nozzles that form a large dot at the same time
increases, power consumed at that time increases.
Head Unit Interval
Head Unit Interval: First Application Example
[0092] FIG. 8 is a plan view of the head unit interval X7 of the
first application example. A4 size sheet of paper S4 is indicated
by bold alternate long and short dash line. For description, the A4
size sheet of paper S4 is used for printing with a resolution of
720 dpi in the paper width direction using both the upstream side
head unit 20A and the downstream side head unit 20B. Note that,
where the length of a nozzle column is 1 inch, when printing is
performed on A4 size sheet of paper, the number of heads that are
arranged in the paper width direction is twelve; however, the
number of heads is four for easier description in the drawing
(hereinafter, the same applies to the other examples).
[0093] In the first application example, the interval X6 is set
between the most upstream side nozzle columns (K column of the head
21A(1) or the head 21A(3), hereinafter referred to as "UU") of the
upstream side head unit 20A and the most upstream side nozzle
columns (K column of the head 21B(1) or the head 21B(3),
hereinafter, referred to as "DU") of the downstream side head unit
20B, and the head unit interval X7 is set so as to be greater than
the length of the short side of the A4 size sheet of paper S4.
[0094] FIG. 9A is a view that shows a state where printing is
performed on the rear end side of A4 size sheet of paper S4 by the
upstream side head unit 20A. When the rear end of the A4 size sheet
of paper S4 faces the most upstream side nozzle columns UU of the
upstream side head unit 20A, the front end of the A4 size sheet of
paper S4 does not face the nozzle columns of the downstream side
head unit 20B. That is, at this time, the maximum number of nozzle
columns that face the A4 size sheet of paper at the same time is
sixteen columns (=4 columns.times.4) that is equal to the number of
nozzle columns included in each head unit.
[0095] FIG. 9B is a view that shows a state where printing is
performed on the front end side and rear end side of A4 size sheet
of paper S4 by the upstream side head unit 20A and the downstream
side head unit 20B. After the rear end of the A4 size sheet of
paper is passed below the most upstream side nozzle columns UU of
the upstream side head unit 20A, the most upstream side nozzle
columns DU of the downstream side head unit 20B face the front end
of the A4 size sheet of paper. That is, after the rear end of the
A4 size sheet of paper is passed below m-th nozzle columns of the
upstream side head unit 20A, the m-th nozzle columns of the
downstream side head unit 20B face the front end side of the A4
size sheet of paper. Therefore, at this time, the maximum number of
nozzle columns that face the A4 size sheet of paper at the same
time is sixteen columns equal to the number of nozzle columns
included in each head unit.
[0096] FIG. 9C is a view that shows a state where printing is
performed on the front end side of A4 size sheet of paper by the
downstream side head unit 20B. When the A4 size sheet of paper
faces all the nozzle columns of the downstream side head unit 20B,
the nozzle columns of the upstream side head unit 20A do not face
the A4 size sheet of paper. Therefore, at this time, the maximum
number of nozzle columns that face the A4 size sheet of paper at
the same time is sixteen columns equal to the number of nozzle
columns included in each head unit.
[0097] That is, the head unit interval X7 of the first application
example is set so that the maximum number of nozzle columns that
face the A4 size sheet of paper at the same time is sixteen columns
equal to the number of nozzle columns included in each head
unit.
[0098] FIG. 10 is a view that shows a first comparative example of
which an interval is reduced as compared with the head unit
interval X7 of the first application example. The head unit
interval X2 of the first comparative example is set so that the
interval X1 between the most upstream side nozzle columns UU of the
upstream side head unit and the most downstream side nozzle columns
of the downstream side head unit (Y column of the head 21B(2) or
the head 21B(4), hereinafter, referred to as "DD") is equal to the
length of the short side of the A4 size sheet of paper S4.
Therefore, in midway of printing, A4 size sheet of paper faces all
the nozzle columns (32 columns=4 columns.times.8) of the upstream
side head unit 20A and downstream side head unit 20B.
[0099] Incidentally, as the number of nozzles that form dots at the
same time, power consumption increases, as described above. In
addition, even in the nozzles that form dots, as the number of
nozzles that form large dots increases, power consumption
increases.
[0100] Therefore, in the first comparative example, power consumed
when ink (large dots) is discharged from all the nozzles of 32
nozzle columns that face the A4 size sheet of paper at the same
time is the maximum power consumption. Similarly, in the first
application example, power consumed when ink (large dots) is
discharged from all the nozzles of 16 nozzle columns that face the
A4 size sheet of paper at the same time is the maximum power
consumption. That is, the maximum power consumption of the first
comparative example is twice the maximum power consumption of the
first application example.
[0101] When the maximum power consumption is large as in the case
of the first comparative example, there is a possibility that a
voltage of the power source portion largely reduces. In this case,
a power failure detection circuit erroneously detects a power
failure and printing operation may be stopped. In order to avoid
the above trouble, a method in which a large capacity power source
is used is employed when the maximum power consumption is large.
However, a large capacity power source is large in shape and
expensive.
[0102] Then, as in the case of the first application example, the
head unit interval X7 is set so that the interval X6 between the
most upstream side nozzle columns UU of the upstream side head unit
and the most upstream side nozzle columns DU of the downstream side
head unit is greater than the short side of the A4 size sheet of
paper. In this case, the number of maximum nozzle columns that face
the A4 size sheet of paper at the same time is sixteen columns
equal to the number of nozzle columns included in each head unit,
so that the maximum power consumption is half the maximum power
consumption of the first comparative example. Therefore, a trouble,
such as interruption of printing operation because of voltage drop,
is eliminated and, as a result, it is unnecessary to use a large
capacity power source.
[0103] In addition, irrespective of the size of the head unit
interval, the A4 size sheet of paper definitely faces all the
nozzle columns (sixteen nozzles) included in each head unit at the
same time. Therefore, the printer 1 needs to have at least a power
source that can allow power consumption when ink (large dots) is
discharged at the same time from all the nozzle columns included in
each of the head unit 20. Therefore, in the present embodiment, the
head unit interval is set so that the maximum number of nozzle
columns that face the A4 size sheet of paper S4 at the same time
does not exceed sixteen columns equal to the number of nozzle
columns included in each head unit 20.
Head Unit Interval: Second Application Example
[0104] FIG. 11A to FIG. 11C are views that show a head unit
interval X8 of a second application example. In the second
application example, as shown in FIG. 11B, the head unit interval
X9 is set so that the most downstream side nozzle columns UD of the
upstream side head unit and the most upstream side nozzle columns
DU of the downstream side head unit is equal to the length of the
short side of the A4 size sheet of paper S4.
[0105] In the initial stage of printing (FIG. 11A), only the
upstream side head unit 20A is used. In the last stage of printing
(FIG. 11C), only the downstream side head unit 20B is used. Then,
in the midway of printing (FIG. 11B), when the rear end of the A4
size sheet of paper S4 faces the most downstream side nozzle
columns UD of the upstream side head unit, the front end of the A4
size sheet of paper S4 faces the most upstream side nozzle columns
DU of the downstream side head unit.
[0106] That is, the head unit interval X9 of the second application
example is set so that the maximum number of nozzle columns that
face the A4 size sheet of paper at the same time is sixteen columns
equal to the number of nozzle columns included in each head unit.
Then, the maximum power consumption of the second application
example is half the maximum power consumption of the first
comparative example, so that the same advantageous effects as in
the case of the first application example are obtained.
[0107] FIG. 12 is a view of a second comparative example of which
an interval is increased as compared with the head unit interval X9
of the second application example. In the second comparative
example, the head unit interval X4 is set so that the interval X3
between the most downstream side nozzle columns UD of the upstream
side head unit and the most upstream side nozzle columns DU of the
downstream side head unit is greater than the length of the short
side of the A4 size sheet of paper S4. In this case, between the
time when the rear end of the A4 size sheet of paper is passed
below the upstream side head unit 20A to the time when the front
end of the A4 size sheet of paper faces the nozzles of the
downstream side head unit 20B (X5), the A4 size sheet of paper is
only transported and no printing is performed thereon. By
performing such an useless transport, transport time (printing
time) becomes long, and the size of the apparatus becomes
large.
[0108] In contrast, in the second application example, before the
rear end of the A4 size sheet of paper is passed below the most
downstream side nozzle columns UD of the upstream side head unit,
the front end of the A4 size sheet of paper face the most upstream
side nozzle columns DU of the downstream side head unit. Therefore,
in the second application example, there is no period of time when
the A4 size sheet of paper does not face the nozzle columns on the
transport belt 12 and, hence, there is no useless transport
period.
[0109] That is, because the head unit interval X9 of the second
application example (FIG. 11B) is set so that the interval X8
between the most downstream side nozzle columns UD of the upstream
side head unit and the most upstream side nozzle columns DU of the
downstream side head unit is equal to or smaller than the length of
the short side of the A4 size sheet of paper, the maximum power
consumption may be reduced as compared with the first comparative
example and the size of the apparatus may be reduced as compared
with the second comparative example as much as possible.
Summary of Setting Method
[0110] When the setting method of the head unit interval according
to the present embodiment is summarized, the head unit interval is
set so that (1) the interval between the most upstream side nozzle
columns UU of the upstream side head unit (upstream side nozzle
group) and the most upstream side nozzle columns DU of the
downstream side head unit (downstream side nozzle group) is greater
than the length of the short side (length in the transport
direction) of a sheet of paper of A4 size (the maximum size to
which liquid can be discharged) and (2) the interval between the
most downstream side nozzle columns UD of the upstream side head
unit and the most upstream side nozzle columns DU of the downstream
side head unit is equal to or smaller than the length of the short
side of the A4 size sheet of paper.
[0111] By setting the head unit interval in conformity to the above
condition, there is no possibility that the maximum number of
nozzle columns that may possibly be used at the same time does not
exceed the number of nozzle columns (sixteen columns) included in
each head unit 20, and, hence, it is possible to suppress the
maximum power consumption to a certain value. In addition, because
there is no useless transport period of time, it is possible to
shorten transport time (printing time) and also possible to reduce
the size of the apparatus.
First Print Method and Second Print Method
[0112] FIG. 13 is a view that shows a state where printing is
performed on an A3 size sheet of paper using the head unit interval
X7 of the first application example. The short side (297 mm) of the
A3 size sheet of paper S3 is made as the length in the paper width
direction, and the long side (420 mm) of the A3 size sheet of paper
S3 is made as the length in the transport direction, and then
printing is performed on the A3 size sheet of paper S3.
[0113] The head unit interval X7 of the first application example
is set so that the short side (210 mm) of the A4 size sheet of
paper S4 is used as a reference. Then, the length of the A3 size
sheet of paper S3 in the transport direction (420 mm) is twice the
length of the A4 size sheet of paper S4 in the transport direction
(210 mm). Therefore, as shown in FIG. 13, the A3 size sheet of
paper S3 faces all the 32 nozzle columns of the upstream side head
unit 20A and downstream side head unit 20B in midway of
printing.
[0114] If ink (large dots9 is discharged from all the nozzles of
the 32 nozzle columns that face the A3 size sheet of paper at the
same time, the maximum power consumption at this time is equal to
the maximum power consumption of the above described first
comparative example. Hence, there may be a trouble that printing
operation is stopped, for example.
[0115] In the present embodiment, when printing is performed on the
A3 size sheet of paper using the head unit interval (first
application example and second application example) that is set
using the short side of the A4 size sheet of paper as a reference,
it is directed to suppress the maximum power consumption to be
lower than "limit power consumption". Here, power consumed when ink
(large dots) is discharged from all the 16 nozzle columns included
in each head unit at the same time is termed as "limit power
consumption". That is, the limit power consumption is equal to the
maximum power consumed when printing is performed on an A4 size
sheet of paper.
[0116] In addition, irrespective of the size of the head unit
interval, the printer 1 needs to have at least a power source that
can allow power consumption when ink (large dots) is discharged
from all the nozzle columns included in each head unit at the same
time. That is, when the maximum power consumption during printing
does not exceed the limit power consumption, it is only necessary
for the printer 1 to include a minimum capacity power source.
[0117] Meanwhile, even when the maximum number of nozzle columns
that face the sheet at the same time exceeds sixteen columns as in
the case of the A3 size sheet of paper, it is possible to suppress
the maximum power consumption to be equal to or lower than the
limit power consumption when the number of nozzle columns that
discharge ink does not exceed sixteen columns. Then, in the present
embodiment, two print methods are used. The two print methods
includes a first print method in which the timing at which ink is
discharged from the nozzles of the upstream side head unit 20A is
the same as the timing at which ink is discharged from the nozzles
of the downstream side head unit 20B, and a second print method in
which the timing at which ink is discharged from the nozzles of the
upstream side head unit 20A is delayed from the timing at which ink
is discharged from the nozzles of the downstream side head unit 20B
and ink is discharged alternately. Hereinafter, a difference
between the first print method and the second print method will be
described.
[0118] FIG. 14 is a view that shows a first driving signal DRV1 and
a second driving signal DRV2. The first driving signal DRV1 is used
for the first print method. The second driving signal DRV2 is used
for the second print method.
[0119] The first driving signal DRV1 is used in the first print
method. The first driving signal DRV1 has one of each of a first
driving pulse W1 and a second driving pulse W2 within a cycle
period T. Then, in accordance with print data, ink is discharged
from each nozzle at an interval of the cycle period T. Therefore,
the time during which one pixel of a printing sheet of paper faces
the nozzle #i is a duration of the cycle period. Specifically, when
the resolution in the transport direction is 720 dpi, the size of a
pixel in the transport direction is 1/720 inch. Hence, in the first
print method, the transport unit 10 transports a printing sheet of
paper so that the printing sheet of paper travels 1/720 inch during
a duration of the cycle period T. The transport speed of this first
print method is set to 2V in this embodiment. Note that the driving
signal DRV shown in FIG. 5 is the first driving signal DRV1.
[0120] Further, the first driving signal DRV1 is of a single type,
and is commonly used for the upstream side head unit 20A and the
downstream side head unit 20B. Therefore, in midway of printing,
even when the sheet of paper S faces both the upstream side head
unit 20A and the downstream side head unit 20B, ink is discharged
at the same time from the nozzles of the upstream side head unit
20A and from the nozzles of the downstream side head unit 20B in
accordance with print data.
[0121] In contrast, the second driving signal DRV2 is formed of two
types. This is because a driving signal used for the upstream side
head unit 20A (hereinafter, referred to as upstream side driving
signal DRV2(A)) is different from a driving signal used for the
downstream side head unit 20B (hereinafter, referred to as
downstream side driving signal DRV2(B)).
[0122] Both driving signals (DRV2(A), DRV2(B)) have the same cycle
period, which is 2T. Then, the time during which one pixel of a
printing sheet of paper faces the nozzle #i is the cycle period 2T.
Hence, in the second print method, the transport unit 10 transports
a printing sheet of paper so that the printing sheet of paper
travels 1/720 inch during the cycle period 2T. The transport speed
of the second print method is set to V. That is, the transport
speed V of the second print method is half the transport speed 2V
of the first print method.
[0123] Further, each of the driving signals (DRV2(A) DRV2(B)) has
one of each first driving pulse W1 and second driving pulse W2.
However, the upstream side driving signal DRV2(A) has two driving
pulses (W1, W2) in a first half period T1 within the cycle period
2T, while the downstream side driving signal DRV2(B) has two
driving pulses in a second half period T2 within the cycle period
2T. Hence, from the nozzles of the upstream side head unit 20A that
uses the upstream side driving signal DRV2(A), ink is discharged in
the first half period T1 within the cycle period 2T. In contrast,
from the nozzles of the downstream side head unit 20B that uses the
downstream side driving signal DRV2(B), ink is discharged in the
second half period T2 within the cycle period 2T.
[0124] Thus, in the second print method, by delaying the period
during which the driving signal has a driving pulse within the
cycle period, ink is alternately discharged from the nozzles of the
upstream side head unit 20A and from the nozzles of the downstream
side head unit 20B.
[0125] Accordingly, first, the controller 50 of the printer 1
receives, from the computer 30, an instruction for performing
printing in the first print method or in the second print method.
When the controller 50 receives an instruction for performing
printing in the first print method, the controller 50 controls the
transport unit 10 so that the transport speed becomes 2V. In
addition, the controller 50 instructs the driving signal generating
circuit 60 of the upstream side head unit 20A and the driving
signal generating circuit 60 of the downstream side head unit 20B
to generate a common first driving signal DRV1.
[0126] On the other hand, when the controller 50 receives an
instruction for performing printing in the second print method, the
controller 50 controls the transport unit 10 so that the transport
speed becomes V. In addition, the controller 50 instructs the
driving signal generating circuit 60 of the upstream side head unit
20A to generate the upstream side driving signal DRV2(A) and
instructs the driving signal generating circuit 60 of the
downstream side head unit 20B to generate the downstream side
driving signal DRV2(B).
[0127] For example, as shown in FIG. 13, the second print method is
used for performing printing on an A3 size sheet of paper using the
head unit interval X7 of the first application example. That is,
printing is performed on the A3 size sheet of paper by alternately
discharging ink from the nozzles of the upstream side head unit 20A
and from the nozzles of the downstream side head unit 20B. In this
manner, as shown in FIG. 13, even when the A3 size sheet of paper
faces all the 32 nozzle columns of the upstream side head unit 20A
and the downstream side head unit 20B in midway of printing, the
maximum number of nozzle columns that discharge ink at the same
time is sixteen columns, so that there is no possibility that the
maximum power consumption exceeds the limit power consumption.
[0128] Moreover, as shown in FIG. 8, the first print method is used
for performing printing on an A4 size sheet of paper using the head
unit interval X7 of the first application example. That is, by
discharging ink at the same time from the nozzle columns of the
upstream side head unit 20A and the downstream side head unit 20B,
both of which face the A4 size sheet of paper at the same time,
printing is performed on the A4 size sheet of paper. When printing
is performed on the A4 size sheet of paper using the head unit
interval X7 of the first application example, because the maximum
number of nozzle columns that face the sheet of paper at the same
time does not exceed sixteen columns, so that the maximum power
consumption does not exceed the limit power consumption. On the
contrary, printing is performed on the A4 size sheet of paper using
the head unit interval X7 of the first application example in the
second print method, printing time will be twice the printing time
of the first print method.
[0129] Then, in the present embodiment, the transport speed is
varied in accordance with "the number of nozzle columns used", and
the first print method and the second print method are
appropriately used. Here, the "nozzle columns used" are nozzle
columns that may possibly discharge ink at the same time. For
example, the nozzle columns used indicate nozzle columns that face
a printing sheet of paper and nozzle columns that face an area of a
printing sheet of paper, on which an image is printed.
[0130] When the number of nozzle columns used is more than the
number of nozzle columns included in each of the upstream side head
unit 20A and the downstream side head unit 20B (predetermined
number=16 columns), the transport speed is reduced and printing is
performed in the second print method. That is, ink is alternately
discharged from the nozzles of the upstream side head unit 20A and
from the nozzles of the downstream side head unit 20B. As a result,
when the maximum power consumption does not exceeds the limit power
consumption, or when the number of nozzle columns used is equal to
or smaller than sixteen columns, the transport speed is increased
and printing is performed in the first print method. That is, ink
is discharged from the nozzle columns used at the same time. As a
result, it is possible to shorten printing time as much as
possible.
[0131] Hereinafter, embodiments in which "nozzle columns used" are
differently defined will be described in detail. Note that a
determination as to whether the first print method is used or the
second print method is used is performed by a printer driver stored
in the memory of the computer 30. The printer driver is a program
that transmits printing image data to the printer 1, for example.
That is, the system in which the printer 1 and the computer 30 that
stores the printer driver therein, which are connected to each
other, is a liquid discharging apparatus.
First Embodiment: Determine Print Method on the Basis of Size of
Printing Sheet of Paper
[0132] In the first embodiment, the printer driver determines a
print method on the basis of "the size of a printing sheet of
paper". For description, the head unit interval of the printer 1 is
the head unit interval X7 of the first application example. Then,
using both the upstream side head unit 20A and the downstream side
head unit 20B, printing is performed with a resolution of 720 dpi
in the paper width direction.
[0133] In the head unit interval X7 of the first application
example shown in FIG. 8, when the length of a printing sheet of
paper in the transport direction is greater than the length (210
mm) of the short side of the A4 size sheet of paper, the front end
of the printing sheet of paper faces the nozzle columns of the
downstream side head unit 20B while the rear end side of the
printing sheet of paper is facing the 16 nozzle columns of the
upstream side head unit 20A. That is, the number of nozzle columns
that face the sheet of paper at the same time exceeds sixteen
columns, which is the number of nozzle columns included in each
head unit. If ink is discharged from all the nozzle columns that
exceed sixteen columns facing the printing sheet of paper, the
maximum power consumption exceeds the limit power consumption.
[0134] Therefore, when the length of the printing sheet of paper in
the transport direction is greater than the length (210 mm) of the
short side of the A4 size sheet of paper, it is necessary to reduce
the maximum power consumption by alternately discharging ink from
the upstream side head unit 20A and from the downstream side head
unit 20B. That is, when the length of the printing sheet of paper
in the transport direction is greater than the length of the short
side of the A4 size sheet of paper, it is possible to prevent the
maximum power consumption from exceeding the limit power
consumption by performing printing in the second print method.
[0135] On the contrary, when the length of the printing sheet of
paper in the transport direction is equal to or smaller than the
length (210 mm) of the short side of the A4 size sheet of paper,
the maximum number of nozzle columns that face the sheet of paper
at the same time does not exceed sixteen columns. Therefore, the
maximum power consumption does not exceed the limit power
consumption, and it is unnecessary to alternately discharge ink
from the upstream side head unit 20A and from the downstream side
head unit 20B. That is, when the length of the printing sheet of
paper in the transport direction is smaller than the length of the
short side of the A4 size sheet of paper, printing is performed in
the first print method. By so doing, it is possible to shorten the
printing time as compared with printing performed in the second
print method.
[0136] FIG. 15 is a flowchart that is executed when the printer
driver determines a print method according to the first embodiment.
First, the printer driver receives image data from various
application software. Then, the printer driver determines whether
the length of the specified printing sheet of paper in the
transport direction is greater than the length (210 mm) of the
short side of the A4 size sheet of paper.
[0137] If the length of the printing sheet of paper in the
transport direction is greater than 210 mm (YES), the printer
driver instructs the printer 1 so as to perform printing on a
printing sheet of paper in the second print method. In addition, if
the length of the printing sheet of paper in the transport
direction is equal to or smaller than 210 mm (NO), the printer
driver instructs the printer 1 to perform printing on a printing
sheet of paper in the first print method. That is, on the basis of
the length of the printing sheet of paper in the transport
direction, the transport speed is determined. Note that the
determined transport speed is never changed while the printing
sheet of paper is being transported.
[0138] In the first embodiment as described above, the printer
driver determines a print method on the basis of the "size of a
printing sheet of paper", and printing is performed in the print
method suitable for the size of the printing sheet of paper.
Because the print method is determined on the basis of the size of
a printing sheet of paper, the print method is determined on the
basis of the number of nozzle columns that face the printing sheet
of paper at the same time, irrespective of ink being discharged or
not discharged in accordance with print data. That is, the "nozzle
columns used" are nozzle columns that face the printing sheet of
paper at the same time. By so doing, the maximum power consumption
during printing does not exceed the limit power consumption, and it
is possible to shorten the printing time as much as possible. In
addition, printing may be performed on a sheet of paper, other than
size (A4 size) that is used as a reference for setting the head
unit interval, the types of paper size that are printable by the
printer 1 are increased.
[0139] As described above, the print method is determined whether
"the length of a printing sheet of paper in the transport direction
is greater than 210 mm". In other words, the print method is
determined on the basis of "the type (size) of a printing sheet of
paper". Because the sizes of almost all printing sheets of paper
are determined in advance according to a standard, so that it is
possible to determine a print method on the basis of "the type of a
printing sheet of paper" at the time when the head unit interval is
set.
[0140] FIG. 16 is one example of a flowchart in which the printer
driver determines a print method on the basis of "a type of a
printing sheet of paper". For example, where types of a printing
sheet of paper that are printable by the printer 1 are A3 size, B4
size, A4 size, and postcard size, the printer driver determines
that printing is performed in the second print method when A3 size
or B4 size, larger than A4 size, is used for printing, and
determines that printing is performed in the first print method
when A4 size or postcard size that is smaller than A4 size is used
for printing. Further, when printing is performed on an irregular
printing sheet of paper, which is defined by a user, the printer
driver determines a print method on the basis of the length of a
printing sheet of paper in the transport direction. Note that the
maximum paper size that is printable by the printer 1 is A3 size;
the flowchart of FIG. 15 and the flowchart of FIG. 16 do not apply
to a case where a printing sheet of paper is larger than A3
size.
[0141] Moreover, the printer driver may be instructed from
application software so as to print a plurality of images as a
single job. In addition, at this time, the size of a printing sheet
of paper may be different depending on images. For example, a
single job contains an image to be printed on an A4 size sheet of
paper and an image to be printed on an A3 size sheet of paper. In
this case, even when that is the same job, the printer driver
detects whether the size of a printing sheet of paper in units of
image and determines a print method.
[0142] Note that the print method is determined using the short
side (210 mm) of the A4 size sheet of paper as a reference, as
described above; however, this does not apply to the case where the
head unit interval of the printer 1 is the head unit interval X9 of
the second application example. Because the head unit interval of
the second application example is greater than the head unit
interval of the first application example, even when a sheet of
paper has a length that is greater than 210 mm in the transport
direction, there is a case where the maximum number of nozzle
columns that face the sheet of paper at the same time does not
exceed sixteen columns.
[0143] Then, when the head unit interval is set greater than the
head unit interval X7 of the first application example, a print
method is determined using the interval X10 between the most
upstream side nozzle columns UU of the upstream side head unit and
the most upstream side nozzle columns DU of the downstream side
head unit as a reference (FIG. 11B). When the length of a printing
sheet of paper in the transport direction is equal to or more than
the interval X10, because the maximum number of nozzle columns that
face the sheet of paper at the same time exceeds sixteen columns,
so that printing is performed in the second print method. Then,
when the length of a printing sheet of paper in the transport
direction is smaller than the interval X10, because the maximum
number of nozzle columns that face the sheet of paper at the same
time is sixteen columns, printing is performed in the first print
method.
Second Embodiment: Determination of Print Method on the Basis of
Image Data
[0144] In the second embodiment, the printer driver determines a
print method on the basis of "image data". For description, the
head unit interval of the printer 1 is the head unit interval X7 of
the first application example.
First Determination Example: Printing of Small Image
[0145] If printing is performed on an A3 size sheet of paper using
the head unit interval X7 that is set using the short side of the
A4 size sheet of paper as a reference, the A3 size sheet of paper
faces all the nozzle columns (32 columns) of both the upstream side
head unit 20A and the downstream side head unit 20B (FIG. 13). When
ink is discharged at the same time from all the 32 nozzle columns
that face the A3 size sheet of paper, the maximum power consumption
exceeds the limit power consumption. However, when the number of
nozzle columns that discharge ink does not exceed sixteen columns,
the maximum power consumption does not exceed the limit power
consumption.
[0146] FIG. 17A is a view that shows a printing area P in which an
image is printed on an A3 size sheet of paper S3. FIG. 17B to FIG.
17E are views that show a state where the image is printed within
the printing area P on the A3 size sheet of paper. The printing
area P is a collection of a plurality of pixels on which dots are
formed, and ink is discharged from nozzles when the printing area P
faces the nozzles.
[0147] Further, the printing area P is indicated by a rectangular
oblique lines in the drawing. A most downstream side pixel column
among pixel columns and a most upstream side pixel column, which
are arranged along the paper width direction in the printing area
P, are respectively denoted as a pixel column L1 and a pixel column
L2. As shown in FIG. 17C, the size of the printing area P in the
transport direction (the length from the pixel column L1 to the
pixel column L2) is smaller than the interval X6 between the most
upstream side nozzle columns UU of the upstream side head unit and
the most upstream side nozzle columns DU of the downstream side
head unit. Then, the image within the printing area P will be
printed in color with a resolution of 720 dpi in the paper width
direction.
[0148] First, as shown in FIG. 17B, an A3 size sheet of paper is
fed so that the pixel column L1 on the A3 size sheet of paper faces
the most upstream side nozzle columns UU of the upstream side head
unit. In the initial stage of printing, ink is discharged from only
the 16 nozzle columns of the upstream side head unit toward the
printing area P.
[0149] Then, when the pixel column L2 faces the most upstream side
nozzle columns UU of the upstream side head unit, the printing area
P does not face the nozzle columns of the downstream side head unit
20B (FIG. 17C). In addition, the front end side of the A3 size
sheet of paper S3 faces the nozzle columns of the downstream side
head unit 20B; however, the front end side of the A3 size sheet of
paper S3 is a blank space, so that no ink is discharged from the
nozzles of the downstream side head unit 20B. Therefore, the A3
size sheet of paper faces the 32 nozzle columns; however, the
nozzle columns that discharge ink are sixteen columns.
[0150] After that, when the pixel column L1 faces the most upstream
side nozzle columns DU of the downstream side head unit, the pixel
column L2 is passed below the most upstream side nozzle columns UU
of the upstream side head unit (FIG. 17D). Therefore, the nozzle
columns that discharge ink do not exceed sixteen columns.
Consequently, ink is discharged from only the 16 nozzle columns of
the downstream side head unit to the printing area P (FIG.
17E).
[0151] That is, when an image is printed within the printing area P
on the A3 size sheet of paper, the A3 size sheet of paper faces all
the nozzle columns (32 columns) of both the upstream side head unit
20A and the downstream side head unit 20B in midway of printing.
However, the number of nozzle columns that discharge ink to the
printing area P at the same time does not exceed sixteen columns.
In other words, even when the number of nozzle columns the face a
printing sheet of paper at the same time exceeds sixteen columns,
there is a case where the number of nozzle columns that discharge
ink at the same time does not exceed sixteen columns depending on
the size of a printing image. In this case, even when printing is
performed in the first print method in which the timing at which
ink is discharged from the nozzles of the upstream side head unit
20A is the same as the timing at which ink is discharged from the
nozzles of the downstream side head unit 20B, the maximum power
consumption does not exceed the limit power consumption.
[0152] Then, in the first determination example, the printer driver
determines a print method not on the basis of "the number of nozzle
columns that face a printing sheet of paper at the same time" but
on the basis of "the number of nozzle columns from which ink is
discharged at the same time". That is, the printer driver
determines on the basis of the number of nozzle columns that face
pixels at which dots are formed on a printing sheet of paper (for
example, printing area P).
[0153] FIG. 18 is a flowchart that is executed when the printer
driver determines a print method in the first determination example
of the second embodiment. First, the printer driver receives image
data from various application software. Then, the printer driver
determines whether the number of nozzle columns that face pixels,
at the same time, at which dots are formed on a sheet of paper is
equal to or smaller than sixteen columns.
[0154] If the number of nozzle columns that face pixels, at the
same time, at which dots are formed on the printing sheet of paper
is equal to or smaller than sixteen columns (YES), the printer
driver instructs the printer 1 to perform printing on a printing
sheet of paper in the first print method. Moreover, if the number
of nozzle columns that face pixels, at the same time, at which dots
are formed on the printing sheet of paper is greater than sixteen
columns (NO) the printer driver instructs the printer 1 to perform
printing on a printing sheet of paper in the second print
method.
[0155] Thus, in the first determination example, the printer driver
detects "the number of nozzle columns that face pixels, at the same
time, at which dots are formed on a printing sheet of paper" from
"image data", and a print method is then determined. That is, "the
nozzle columns used" are nozzle columns that face, at the same
time, an area on the printing sheet of paper, to which ink is
discharged. By so doing, the number of nozzle columns that
discharge ink at the same time does not exceed sixteen columns, and
the maximum power consumption during printing also does not exceed
the limit power consumption.
[0156] Then, the case where the number of nozzle columns that face
pixels, at the same time, at which dots are formed on a printing
sheet of paper is equal to or smaller than sixteen columns, is a
case where a relatively small image is printed. For example, as
shown in FIG. 17A, an image, or the like, of which the length of a
printing area in the transport direction is equal to or smaller
than the length of the short side of the A4 size sheet of paper.
That is, the transport speed is determined on the basis of the
length of an image in the transport direction. Note that the
determined transport speed is never changed while the printing
sheet of paper is being transported. FIG. 17F is one example of a
relatively small image P2. The length of the image P2 in the
transport direction is greater than the length of the short side of
the A4 size sheet of paper, but the image P2 is located only on the
left side half of the A3 size sheet of paper. In this case, ink is
discharged only from both the left side half nozzle columns of the
upstream side head unit 20A and the left side half nozzle columns
of the downstream side head unit 20B, and the number of nozzle
columns that discharge ink does not exceed sixteen columns.
[0157] Note that when the head unit interval is determined using
the A4 size sheet of paper as a reference, the number of nozzle
columns that face a printing sheet of paper having a size equal to
or smaller than A4 size at the same time does not exceed sixteen
columns. Therefore, the first determination example may only be
applied to a size larger than A4 size.
[0158] Furthermore, in contrast with the first determination
example, a print method is determined on the basis of "the size of
a printing sheet of paper" in the first embodiment. That is, in the
first embodiment, even when the number of nozzle columns that
discharge ink at the same time does not exceed sixteen columns,
when the size of a printing sheet of paper is A3 size, printing is
performed in the second print method. Because the transport speed
of the first print method is twice the transport speed of the
second print method, when a small image is printed, it is possible
to shorten the printing time in the first determination example
more than that of the first embodiment. However, because the first
determination example detects the number of nozzle columns that
discharge ink in each pieces of image data, a determination method
of a print method by the printer driver is more complicated than
that of the first embodiment.
Second Determination Example: Monochrome Printing
[0159] The heads 21 of the printer 1 of the present embodiment
includes nozzle columns of four colors YMCK, so that both color
printing and monochrome printing may be performed. Then, when in
monochrome printing, only black ink is used.
[0160] When printing is performed on an A3 size sheet of paper with
a resolution of 720 dpi in the paper width direction using the head
unit interval X7 of the first application example, the sheet of
paper faces all the nozzle columns (32 columns) of both the
upstream side head unit 20A and the downstream side head unit 20B
(FIG. 13). If this is color printing, there is a possibility that
ink is discharged from all the 32 nozzle columns that face the A3
size sheet of paper. As a result, the maximum power consumption
exceeds the limit power consumption. However, if it is monochrome
printing, ink is discharged only from black nozzles K of eight
columns (=32/4) among the 32 columns that face the A3 size sheet of
paper. That is, the maximum number of nozzle columns from which ink
is discharged at the same time is eight columns. Even when ink is
discharged from the nozzles of both the upstream side head unit 20A
and the downstream side head unit 20B at the same time, the maximum
power consumption does not exceed the limit power consumption.
[0161] Then, in the second determination example, the printer
driver detects, on the basis of data of a print mode in image data,
"whether it is monochrome printing or color printing" and then
determines a print method.
[0162] FIG. 19 is a flowchart that is executed when the printer
driver determines a print method in the second determination
example. First, the printer driver receives image data from various
application software. Then, the printer driver detects whether an
image is printed with monochrome or an image is printed with
color.
[0163] If the image is printed with monochrome (YES), the printer
driver instructs the printer 1 to perform printing on a printing
sheet of paper in the first print method. On the other hand, if the
image is printed with color (NO), the printer driver instructs the
printer 1 to perform printing on a printing sheet of paper in the
second print method. That is, the transport speed in color printing
(when first liquid and second liquid are discharged) is lower than
the transport speed in monochrome printing (the first liquid is
discharged but the second liquid is not discharged). Note that the
transport speed is never changed while the printing sheet of paper
is being transported.
[0164] In the second determination example as described above, the
printer driver detects, on the basis of "image data" whether "an
image is printed with monochrome or an image is printed with color"
and then determines a print method. By so doing, the maximum power
consumption during printing does not exceed the limit power
consumption.
Third Determination Example: Low-Resolution Printing
[0165] The printer 1 of the present embodiment is able to perform
printing with a high resolution (720 dpi in the paper width
direction) using both the upstream side head unit 20A and the
downstream side head unit 20B and is able to perform printing with
a low resolution using any one of the upstream side head unit 20A
and the downstream side head unit 20B.
[0166] When a color image is printed on an A3 size sheet of paper
using the head unit interval X7 of the first application example,
the sheet of paper faces all the nozzle columns (32 columns) of
both the upstream side head unit 20A and the downstream side head
unit 20B (FIG. 13). If printing is performed with 720 dpi in the
paper width direction at this time, there is a possibility that ink
is discharged from all the nozzle columns that face the A3 size
sheet of paper. As a result, the maximum power consumption exceeds
the limit power consumption. However, if printing is performed with
360 dpi in the paper width direction, ink is discharged only from
any one of the upstream side head unit 20A and the downstream side
head unit 20B. At this time, the maximum number of nozzle columns
from which ink are discharged is sixteen columns, and the maximum
power consumption does not exceed the limit power consumption, so
that it is not necessary to alternately discharge ink from the
upstream side head unit and the downstream side head unit. That is,
when in a low-resolution printing, by performing printing in the
first print method, it is possible to shorten the printing
time.
[0167] Then, in the third determination example, the printer driver
determines a print method on the basis of "resolution in the paper
width direction" from data of a print mode in image data.
[0168] FIG. 20 is a flowchart that is executed when the printer
driver determines a print method in the third determination
example. First, the printer driver receives image data from various
application software. Then, the printer driver detects resolution
in the paper width direction.
[0169] If printing is performed with a resolution of 360 dpi in the
paper width direction (low-resolution printing) (YES), the printer
driver instructs the printer 1 to perform printing on a printing
sheet of paper in the first print method. On the other hand, if
printing is performed with a resolution of 720 dpi in the paper
width direction (high-resolution printing) (NO), the printer driver
instructs the printer 1 to perform printing on a printing sheet of
paper in the second print method. That is, the transport speed when
printing is performed with a high resolution using both the
upstream side head unit 20A and the downstream side head unit 20B
is lower than the transport speed when printing is performed with a
low resolution using any one of the upstream side head unit 20A and
the downstream side head unit 20B. Note that the transport speed is
never changed while the printing sheet of paper is being
transported.
[0170] In the third determination example as described above, the
printer driver detects, on the basis of "image data" whether "an
image is printed with a low resolution or an image is printed with
a high resolution" and then determines a print method. By so doing,
the maximum power consumption during printing does not exceed the
limit power consumption, and it is possible to shorten the printing
time.
Third Embodiment: Change in Print Method in Midway of Printing
[0171] The number of nozzle columns that face a printing sheet of
paper changes with time while the printing sheet of paper is being
transported. In the third embodiment, a print method is changed "in
midway of printing of one printing sheet of paper". For
description, the head unit interval of the printer 1 is the head
unit interval X7 of the first application example, and a color
image is printed with a resolution of 720 dpi in the paper width
direction on an A3 size sheet of paper. FIG. 21A to FIG. 21C are
views that show a state where an A3 size sheet of paper S3 is
transported. FIG. 22A is a view that shows a relationship between
the number of nozzle columns that face the A3 size sheet of paper
and transport time.
[0172] The front end of the A3 size sheet of paper initially faces
two most upstream side nozzle columns UU of the upstream side head
unit. Then, as the A3 size sheet of paper is transported, the
number of nozzle columns that face the A3 size sheet of paper
increases and, at time T1, the A3 size sheet of paper faces the 16
nozzle columns of the upstream side head unit (FIG. 21A).
[0173] After that, until time T2 at which the front end of the A3
size sheet of paper faces the most upstream side nozzle columns DU
of the downstream side head unit, the number of nozzle columns that
face the A3 size sheet of paper does not increase and sixteen
columns are maintained to face the A3 size sheet of paper. Then,
from time T2, the number of nozzle columns of the downstream side
head unit, which face the front end side of the A3 size sheet of
paper, increases.
[0174] Thereafter, at time T3, the A3 size sheet of paper faces all
the nozzle columns (32 columns) of both the upstream side head unit
and the downstream side head unit (FIG. 21B). The number of nozzle
columns that face the A3 size sheet of paper does not increase more
than 32 columns. From time T4 at which the rear end of the A3 size
sheet of paper is passed below the most upstream side nozzle
columns UU of the upstream side head unit, the number of nozzle
columns that face the A3 size sheet of paper gradually reduces.
[0175] From print start time T0 to time T2, the A3 size sheet of
paper faces only the upstream side head unit 20A. Therefore, even
when ink is discharged from all the nozzles of the 16 nozzle
columns that face the A3 size sheet of paper at this time, the
maximum power consumption does not exceed the limit power
consumption.
[0176] However, from time T2, the number of nozzle columns that
face the A3 size sheet of paper exceeds sixteen columns, if ink is
discharged from all the nozzle columns that face the A3 size sheet
of paper at the same time, the maximum power consumption exceeds
the limit power consumption.
[0177] However, from time T5, the A3 size sheet of paper faces only
the downstream side head unit 20B. Therefore, the number of nozzle
columns that face the A3 size sheet of paper is again equal to or
smaller than sixteen columns, so that the maximum power consumption
does not exceed the limit power consumption.
[0178] Then, in the third embodiment, when the A3 size sheet of
paper faces only one of the upstream side head unit and the
downstream side head unit (from T0 to T2, and from T5 to T7), it is
not necessary to alternately discharge ink from the upstream side
head unit and from the downstream side head unit, so that printing
is performed in the first print method. Then, when the A3 size
sheet of paper faces both the upstream side head unit and the
downstream side head unit (from T2 to T5), printing is performed in
the second print method in which ink is alternately discharged from
the upstream side head unit and from the downstream side head unit.
That is, the transport speed changes while a printing sheet of
paper is being transported. By so doing, the maximum power
consumption does not exceed the limit power consumption. Note that,
in the first embodiment and in the second embodiment, the transport
speed does not change while a printing sheet of paper is being
transported. Then, the transport speed is determined on the basis
of the maximum number of nozzle columns among "the number of nozzle
columns used" that changes while a printing sheet of paper is being
transported.
[0179] FIG. 22B is a view that shows changes in transport speed
while printing is being performed on an A3 size sheet of paper. At
time T2 at which the number of nozzle columns that face the A3 size
sheet of paper exceeds sixteen columns, the print method is
switched from the first print method to the second print method
and, thereby, the transport speed reduces from 2V to V. At time T5
at which the number of nozzle columns that face the A3 size sheet
of paper is again equal to or smaller than sixteen columns, the
print method is switched from the second print method to the first
print method and, thereby, the transport speed increases from V to
2V. In addition, as in the case of the transport speed, as the
print method is switched, the driving signal generated in each
driving signal generating circuit also changes.
[0180] In regard to timing at which the print method is switched,
that is, timing (T2) at which the A3 size sheet of paper initiates
to face the downstream side head unit, or timing (T5) at which the
A3 size sheet of paper is passed below the upstream side head unit,
a position of the A3 size sheet of paper is managed using a sensor,
or the like. For example, time T8 from when the A3 size sheet of
paper is detected by the paper detecting sensor 41 shown in FIG. 2A
to when the front end of the A3 size sheet of paper faces the
downstream side head unit may be obtained in advance. Then, the
print method may be switched after time T8 has elapsed from when
the A3 size sheet of paper is detected by the paper detecting
sensor 41.
[0181] In the third embodiment as described above, by switching the
print method "while printing is being performed on one printing
sheet of paper", the number of nozzle columns from which ink is
discharged at the same time does not exceed sixteen columns, and
the maximum power consumption during printing does not exceed the
limit power consumption. Furthermore, because, in the initial state
and last stage of printing, printing is performed in the first
print method in which the transport speed is high, it is possible
to shorten the printing time as compared with the first embodiment
in which the A3 size sheet of paper is printed only in the second
print method.
[0182] Note that, at time T2 in FIG. 22B, the transport speed is
instantaneously reduced to half, but it is not limited to it.
Actually, it is difficult to instantaneously change the transport
speed to a target speed, and it takes some time to converge on the
target speed. Therefore, immediately after the transport speed is
changed, there is a possibility that a printing sheet of paper is
not transported by a predetermined amount and, thereby, dots are
not formed at appropriate positions. As a result, portions at which
dots are not appropriately formed appear as stripes on an image,
thus deteriorating image quality.
[0183] Then, by gradually approximating the transport speed to half
the transport speed, it is possible to reduce deterioration of
image quality. This is because a transport error is smaller when
the transport speed is gradually reduced to half than when the
transport speed is instantaneously reduced to half, and, thereby,
deviation of dots from appropriate positions also becomes minute.
However, in this case, until the transport speed is reduced to half
the speed, it is not allowed to switch from the first driving
signal DRV1 to the second driving signal DRV2 (FIG. 14), so that it
is necessary to, for example, delay the driving signal as the
transport speed is gradually reduced.
Alternative Embodiments
[0184] In the above described embodiments, it is mainly described
as to a printing system that includes an ink jet printer; however,
a method of reducing maximum power consumption, or the like, is
also included in the disclosure. In addition, the above described
embodiments are intended to easily understand the aspects of the
invention and are not used to limit the scope of the invention. The
invention may be modified or improved without departing from the
scope of the invention, and, of course, the invention also
encompasses equivalents thereof. For example, the following
alternative embodiments may also be included in the scope of the
invention.
Head Unit Interval
[0185] In the above described embodiments, the head unit interval
is set so that the short side of the A4 size sheet of paper is used
as a reference, and, when printing is performed on the A3 size
sheet of paper, the transport speed is reduced without changing the
head unit interval; however, it is not limited to it. For example,
the head unit interval may be variable. That is, the upstream side
head unit and the downstream side head unit may be moved relatively
in the transport direction. By so doing, in conformity with the
size of a printing sheet of paper, it is possible to change the
head unit interval so that the maximum power consumption is
suppressed to a certain value. Note that the head unit interval may
be moved by a printer or by a user. As a result, types of printable
paper size are increased. Then, it is only necessary to reduce the
transport speed only when the number of heads that face a printing
sheet of paper at the same time is large and the maximum power
consumption becomes large even with a maximum head unit
interval.
First Embodiment and Second Embodiment
[0186] In the above described second embodiment and the third
embodiment, the printer driver determines a print method using one
item as a reference; however, it is not limited to it. For example,
a plurality of reference items may be combined for determining a
print method. FIG. 23 is one example of a flowchart that is
executed in the case where a plurality of reference items are
combined. At first, the printer driver determines (second
determination example, third determination example) whether
printing can be performed in the first print method on the basis of
data of a print mode (color of printing, resolution). Then, the
printer driver determines whether printing can be performed in the
first print method on the basis of paper size (first embodiment).
Finally, the printer driver determines whether printing can be
performed in the first print method on the basis of the size of an
image to be printed (first determination example). Because a method
of determining a print method on the basis of the size of an image
is complicated, when it is confirmed that printing can be performed
in the first print method using items other than the item using the
size of an image, it is possible to determine a print method more
quickly than to confirm the sizes of all images.
Printer Driver
[0187] In the above described embodiments, a print method is
determined at the printer driver side in the computer 30; however,
it is not limited to it. For example, the controller 50 of the
printer 1 may be configured to determine a print method. In this
case, only the printer is a liquid discharging apparatus.
Ink Jet Line Head Printer
[0188] In the above described embodiments, the ink jet line head
printer is used as a liquid discharging apparatus, for example;
however, it is not limited to it. The aspects of the invention may
be applied to various industrial apparatuses, other than the
printer (printing apparatus). For example, the invention may be
applied to any liquid discharging apparatuses, such as a color
filter manufacturing apparatus, a display manufacturing equipment
for an organic EL display, or the like, a semiconductor
manufacturing equipment, a DNA chip manufacturing equipment, a
circuit board manufacturing equipment, and a printing equipment for
printing a pattern on a cloth, or the like, other than the printer
(printing apparatus). In addition, the printer of the above
described embodiments applies a voltage to a driving element
(piezoelectric element) to expand/contract an ink chamber, thus
discharging liquid. However, it is not limited to it. For example,
the printer may be configured to discharge liquid using bubbles
generated in a nozzle by means of electric heating element.
High-Resolution Printing
[0189] In the above described embodiments, high-resolution printing
is enabled in such a manner that nozzle columns of the downstream
side head unit 20B is offset at a half nozzle pitch in the paper
width direction relative to the nozzle columns of the upstream side
head unit 20A; however, it is not limited to it. For example, the
nozzle columns of the upstream side head unit 20A and the
downstream side head unit 20B need not be offset in the paper width
direction. By alternately forming dots (overlapping print) from the
nozzles #i of the upstream side head unit 20A and the nozzles #i of
the downstream side head unit 20B, which are arranged in the
transport direction, for forming raster lines along the transport
direction, it cannot perform high-resolution printing but it is
possible to reduce deterioration of image quality when nozzle
missing is present, or the like.
Number of Head Units
[0190] In the above described embodiments, a method of setting an
interval between two head units, that is, the upstream side head
unit 20A and the downstream side head unit 20B, is described, for
example; however, it is not limited to it. For example, even when
three head units are used, the aspects of the invention may be
applied to setting an interval between the head units.
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